I've run a couple sessions of shadow dark now and i really like it.
I feared players would be bored because character progression is very random and mechanics are very simple, but so far that's not the case, there is way more "oh maybe we could jam that door with some of the bones in this sarcaphogus" and "we might be able to get into the spooky temple if we get our hands on some cultists robe" and way less looking up skills and spells.
I also spend way less time prepping specific encounters, because 'balance' is not expected and my players tend to tackle situations very different from what i expected, so i have more time to think about the people they've met or tie things together that started as random encounters and things happening in the background that they might stumble over.
as for running 'an OSR game' that will look different for everbody else, some people will dive in to a different dungeon every session, others will spend a lot of time in a city talking to people, gathering clues about old dangerous places or dragon kidnapping princesses and a dungeon is more of a giatn set piece, the only things that i find to be common in OSR are:
- have fun.
- Rulings over rules, if it seems right to ask for a check with a dc of 12 in a given situation that's what will be done even if there is a rule stating the dc should be 14 and the players gets advantage. we are here to have fun and not stopping every 15 minutes just to see if we have fun the 'proper' way.
- combat is not the default state of an encounter. Orcs don't just teleport in surrounding you, the encounter starts with the players noticing them and they might not be out for blood, they could be paid off with some rations, or they could be avoided entirely, or they are fleeing from an owlbear.